An essay on the physiology of the iris : with a different view of its relations and sympathies from the one usually received : and an attempt to establish a new theory of the action of light upon the eye / by John Walker.

  • Walker, John, 1731-1803.
Date:
1833
Catalogue details

Licence: Public Domain Mark

Credit: An essay on the physiology of the iris : with a different view of its relations and sympathies from the one usually received : and an attempt to establish a new theory of the action of light upon the eye / by John Walker. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    child exposed its eyes voluntarily to the light, and followed tlie movements of a watch, which was held up hefore it. Mr. Lawrence says of two cases which he has seen—they did not hear exposure to light well, an expression that would scarcely lead one to suppose that there was much dread of light. In one instance, quoted from a foreign writer,* nothing is mentioned of this except the term weakness of sight can he so considered. In anotherf there was only a rudiment of an Iris at the lower margin of the cornea. The full light of day was offensive to him, and his sight had become im- , paired lately^ &c. This person had also three daughters who had no Iris, these did not bear the light so well, but still appear to have had some degree of vision. These cases seem evidently to point more to an optical deficiency, and the inconveniences resulting from a want of power to regulate the entrance of light into the bottom of ; the eye, than any intolerance of light considered as a stimulus. ' The state termed mydriasis, in which the pupil is always broadly dilated, may be noticed. In individuals thus affected, there is no gi'eater sensibility to light than in others, but their vision is not perfect: they require optical assistance. The action of belladonna, &c. upon the Iris produces, temporarily^ a state similar to the two last mentioned. Sometimes the pupil is so dilated as to reduce the Iris to a mere circle around the ciliary margin. Nothing but imperfection of vision is observed, no intole- rance of light is complained of. The confusion of vision following a sudden change, from a dilated to a contracted state of the pupil, seems to be accounted for by the momentary derangement of the optical focus. Instead of sympathy existing between the Retina and Iris, we find extensive evidences of a close and intimate relation between the latter and the external parts of the eye and eyelids. In proof of this we may again refer to sleep. What is the condition of the eyelids ? They are closed. What is the state of the pupil ? It is contracted. When the eye is exposed to a strong light, or on looking at a minute or near object, the same thing happens ; here the Iris acts in sym- pathy with the parts supplied with the fifth nerve, the orbiculai-is palbrebrarum, corrugator supercilii, &c. which all contract to defend the eye. This action is also observed in inflammation of the brain. » Baratta. + lu Ammou's Zeitsciirift.